A 19-year-old Texas cheerleader was raped and murdered by her boyfriend, who in the one month they were dating flew into at least one steroid-induced rage, authorities said.

Mark Phillip Howerton turned himself in Wednesday in connection with the death of Cayley Mandadi, who was covered head to toe in bruises, nude from the waist down and unconscious when Howerton dumped her at a hospital in October, My San Antonio reported.

Howerton’s story of what happened that night didn’t match up with Mandadi’s injuries, which were consistent with sexual trauma, an arrest warrant affidavit said.

The 22-year-old — who witnesses told cops has flown into a “roid rage” before — tried to claim Mandadi stopped breathing after the couple had “rough” makeup sex at a gas station just outside San Antonio.

But a medical exam showed the Trinity University cheerleader had two black eyes and bruises and scratches all over her body, including to her neck and thighs.

“The only areas of [Mandadi] with no evidence of injury were her back and the back of her legs,” the affidavit said.

She was pronounced brain-dead Oct. 30. She died after being taken off life support the next day.

The tragic turn of events began at the Mala Luna music festival in San Antonio the day before Mandadi died. She and Howerton spent the weekend doing ecstasy and drinking Crown Royal whiskey and got into a fight when they encountered her ex-boyfriend at the festival.

The couple took their argument to the car. Once things were smoothed over, Mandadi agreed to go to Houston with Howerton, he told investigators.

But none of her belongings were found in Howerton’s car, other than the clothes she was wearing that day, showing that she hadn’t packed for the trip, the warrant said. Howerton claimed he planned on buying her everything she needed.

Howerton also claimed Mandadi told him he was her soul mate and vowed to drop out of college to be with him, the warrant said.

It was on the way to Houston when Howerton said the couple had “rough” but consensual sex in the car, including “hair-pulling, light choking and scratching,” the warrant said.

Howerton told authorities that afterward, Mandadi complained about not feeling well and climbed into the passenger seat without her clothes on as Howerton continued the drive.

At some point, near Luling, the boyfriend claimed he noticed Mandadi wasn’t breathing and attempted to do CPR on her before detouring to a nearby hospital.

At the hospital, police took photos of Howerton, who had scratches on his forearms and knuckles that were “red in a manner consistent with someone punching someone else,” the warrant stated.

Her cause of death was later determined to be blunt force trauma to the head.

A friend of Howerton’s told authorities in January that Howerton allegedly admitted that he “lied to police, had ‘very rough’ sex in a mall/movie parking lot with [Mandadi] that night, where he choked and slapped” her.

He also told the pal he didn’t know how long she wasn’t breathing and that cops hadn’t found his burner phone that was hidden inside a planter at the hospital.

Mandadi had previously told her sorority sisters and ex-boyfriend that Howerton had physically abused her and threatened her in the past.

Friends told Texas Rangers that Howerton trashed Mandadi’s dorm room in September and that he later blamed the incident on “roid rage.” Other friends said Howerton sold steroids on campus at Trinity.

Witnesses also detailed other instances of Howerton’s violence, including slamming Mandadi’s head into a car window, waving a gun in her face and threatening to toss her off a balcony.

Howerton faces up to life in prison on murder, aggravated sexual assault and criminal mischief charges.

“Mr. Howerton is ready and eager to vindicate himself in court. He’s innocent of the charges, and he’s doing the right thing,” said his lawyer, John Hunter. “If someone has a warrant out for his arrest, then he needs to turn himself in.”